#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <unistd.h>
#include <time.h>

int main(int argc, char *argv[]) {
  int len, i, rseed;
  char *data="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789",
	buffer[1024];
  FILE *frand;

  if ((frand = fopen("/dev/urandom", "r")) != NULL) {
    for (i=0; i<10; i++) rseed += fgetc(frand);
    fclose(frand);
  } else rseed = 1;

  srandom((int)time(NULL)*getpid()&rseed);
  memset(buffer, 0, 1024);

  if (argc < 2) len = 20;
  else len = atoi(argv[1]);

  for (i=0; i<len; i++)
    buffer[i] = data[random()%(strlen(data))];

  printf("%s\n", buffer);

  return 0;
}